1. Field of the Invention
The present invention relates to deflashing apparatus and more particularly to cryogenic deflashing apparatus for removing flash and burrs from molded articles or parts in a low temperature environment by bombarding the articles with a high velocity media stream.
2. Description of the Prior Art
The molding of articles from plastic, rubber and other materials generally leaves a residual flash on the article in the area adjacent the interfacing mold surfaces. Such flash is functionally and aesthetically objectionable. The removal of such flash by hand trimming is costly and sometimes difficult.
To eliminate the hand trimming operation deflashing apparatus has been developed which cools the flash to the embrittlement point and then subjects the articles to a high velocity stream of pellets, commonly referred to as the blasting or deflashing media. To cool the flash to the embrittlement point the prior art apparatus injects cryogenic liquids, such as liquid nitrogen directly into a chamber in which the deflashing media is propelled against the articles or through which the articles are conveyed on their way to a deflashing area or station. See U.S. Pat. Nos. 4,355,488 and 4,030,247. The cryogenic liquid vaporizes by exchanging heat with the articles, atmosphere and surrounding structures. Since the energy required to produce liquid cryogens is substantial the use of such prior art apparatus is expensive.
In addition cryogens used in the prior art apparatus displace the ambient air and create an asphyxiating atmosphere within and surrounding the deflashing chamber. As a result of the substantial safety hazzards posed by the cryogenic environment some of the prior art apparatus have incorporated expensive systems such as automatically operated doors for permitting articles to be inserted and removed from the deflashing area (see the '488 patent noted above) to minimize the leakage of cryogen into the surrounding atmosphere. While such doors may reduce the safety hazzard for the area surrounding the deflashing chamber, they do not reduce the hazzard posed to personnel required to gain entrance to the chamber for maintenance purposes.
The prior art apparatus also has certain deficiencies with respect to the effecient and thorough removal of flash. Many molded articles have flash on only one side. The prior art apparatus has typically employed conveyor systems which indescriminately present either side of an article to the media blast pattern depending upon how the article was placed on the conveyor. Other prior art conveyor systems have been arranged to tumble or rotate the article or parts as they are carried through the deflashing chamber. In the first case inconsistent and unsatisfactory deflashing may result. In the second case the time required to remove the flash may be unduly high for articles with flash located primarily or solely on one side. Such an increased exposure time increases the overall production time and cost. In addition the increased exposure of the main body of the article to the low temperature environment and deflashing media increases the possibility of damage to the article.
The above deficiencies of the prior art apparatus are overcome by the present invention.